Samson A. Jenekhe

Synthesis of Highly Conducting Heterocyclic F'olycarbazoles by Simultaneous Polymerization and Doping In Liquid Iodine

Abstract Electrically conducting iodine complexes of homopolymers and copolymers of poly(N-akyl-3,3 ‘carbazolyl) are prepared by simultaneous polymerization and doping of N-akyl- and dihalo-derivatives of carbazole in liquid iodine. This represents a direct one-step chemical method of preparing doped conducting polymers from the monomers and dopants analogous to the electrochemical synthetic technique. The amorphous black polymer complexes are stable in air and can be melt cast into films with conductivity in the range 10−-3 to 1 ohm−1cm−1. Preliminary results of Thermal Analysis, FTIR Spectroscopy, and Gel Permeation Chromatography have provided insights into the mechanism and kinetics of polymerization and polymer structures. X-ray Photoelectron Spectroscopy (XPS) data has provided evidence of transfer of charge from the carbazole unit in the polymer complexes.

FLOW AND FILM THICKNESS OF BINGHAM PLASTIC LIQUIDS ON A ROTATING DISK

The free surface film flow of Bingham plastic liquids on a rotating disk has been analyzed theoretically. It is shown that the Bingham plastic material in the inner core of radius rr remains.stressed below the yield value and behaves as an elastic solid. The fluid in the region r > rc is further separated by a yield surface into a region of shear flow adjacent lo the surface of the disk and a region of plug flow near the free surface. The film thickness profile and yield surface were evaluated numerically. The results show that it is impossible to produce radially uniform thin films from liquids which have a yield stress using the spin coating deposition (SCD) technique. The results further provide a rheological explanation of the 1922 observations of Walker and Thompson on the uniformity of films produced on substrates by SCD. An experimental film thickness profile of a liquid with a yield stress shows good qualitative comparison with predicted profiles

Synthesis and studies of poly(3,9-carbazolyl), a new conductive polymer displaying high optical transmittance in the visible

Abstract A polycarbazole consisting mostly of 3,9 linkages has been synthesized in a DMF solution by coupling 3,6-diiodocarbazole with an activated copper catalyst. Although this polymer cannot be oxidized by I2, other acceptors such as iodine monochloride or NO+ will convert it to a p-type semiconductor with a conductivity as high as 1 ohm−1 cm−1. A unique property of the oxidized polymer complex is that it displays a maximum transmittance in the visible at 600 nm and a broad near-i.r. band at 2300 nm. In a rigorously oxygen- and water-free environment, coupling between radical cations on adjacent chains produced by NO+ oxidation takes place at the remaining iodine-substituted 6,6′ positions. The 2300 nm band disappears in favor of a band at 900 nm in the crosslinked material. The decomposition pathway for bromine or ICl-oxidized material, however, involves halogenation of the ring. The large shift of the long-wavelength absorbance of the radical cation on the 3,9-linked polymer versus that found on the carbazole monomer suggests that a significant number of adjacent carbazole units are close to planarity. This must provide a significant pathway for electronic transport.

Electrically conducting complexes of poly(3,6-N-methylcarbazolyl methylene

Abstract Poly(3,6- N -methylcarbazoly methylene) prepared by acid-catalysed condensation polymerization of N -methylcarbazole with formaldehyde exhibits p-type semiconducting properties when doped with electron acceptors such as iodine, bromine, nitrosyl tetrafluoroborate and nitrosyl hexafluoroantimonate. The polymer samples have T g in the range 100 – 148 °C, chain length in the range 13 – 25, and a molecular weight distribution of 1.17 –1.51. The polymer complexes with dopant anion (I 3 − , Br 3 − , BF 4 − ) to polymer repeating unit ratio of 0.67 – 0.95 have a d.c. conductivity of 10 −3 to 10 −1 ohm −1 cm −1 and a positive thermoelectric voltage at 23 °C. An important new feature of the methylene-bridged polycarbazole conducting polymers is doping-induced polymer backbone conjugation of the form ue5f8CH 2 ue5f8→=CHue5f8. Evidence for this oxidation mechanism, converting methylene linkage to methine linkages, includes elemental analysis, infrared spectra, proton NMR and electron spin resonance results.

The Role of Polymer Cations in The Polymerization and Electrical Conductivity of Polycarbazole

Abstract The high electrical conductivities (lohm−1cm−1) in 3,3’ polycarbazole charge transfer complexes originate from hopping of radical cations delocalized over only two carbazole units. Although some intramolecular transport must occur a significant intermolecular hopping component must be present. In fact there is significant evidence from model compound studies that distinct bound states exist between radical cations on adjacent chains. The radical cations in the N-methyl substituted polymers are so stable that the conductivity remains unchanged for months in air. These same radical cations can propagate a polymerization reaction through exposed chain ends in molten iodine or bromine solvents. Polymerizations, charge transfer doping, solvent casting thus can be carried out by simply dissolving monomer in the molten halogen. The polymerizing liquid iodine solutions can be reduced by S2O4,= to produce neutral polymer.

Optical Power Limiting Behavior Of Novel Nonlinear Optical Polymers

Optical power limiting behavior is demonstrated in several nonlinear optical polymers and organic model compounds that exhibit third-order optical nonlinearities. A remarkably sharp intensity-limiting behavior was observed in nonlinear transmission measure-ments of output versus input intensities at 1064 nm laser light without an aperture. The soluble novel organic polymers were found to exhibit both absorptive and refractive nonlinear optical effects that were evidenced by nonlinear absorption and temporal pulse steepening measurements. Nonlinear absorption coefficient (α2) and nonlinear index of refraction (n2) as high as 10 -7 cm/W and 10 -11 cm respectively were obtained at 1064 nm using a nanosecond Q-switched Nd:YAG laser. The observed nonlinearities decreased when measured with a 35 picosecond mode-lock laser. However, since the observed nonlinearities were independent of the energy density of the laser irradiation, it is suggested that the nonlinear mechanism is not thermal in origin. Solutions and solid films of the organic materials were studied. Intensity-limiting thresholds as low as 10 MW/cm2 and laser damage threshold greater than 10 GW/cm2 were obtained. It is suggested that nonlinear optical polymers hold promise for applications in passive optical limiting and regulating devices.

Protective group synthesis of poly-N-hydro-(3,6-carbazolyl)☆

Abstract Poly-N-trityl-(3,6-carbazolyl), PNTPMCZ, has been synthesized in pyridine solution using an activated nickel catalyst. 9-Trityl-3,6-diiodocarbazole was polymerized and the triphenylmethyl group subsequently removed by acid hydrolysis. The N-protected monomer was made by a phase-transfer reaction employing 3,6-diiodocarbazole, a benzotriethylammonium chloride catalyst, basic solution and triphenylmethyl chloride. A wide variety of N-substituents can be obtained in this way, allowing the molecular design of polycarbazolyls to be controlled. In addition, weakly-bound N-substituents can be employed for solubility enhancement during reaction and subsequently partially or fully cleaved from the polymer by acid hydrolysis. Poly-N-hydro-(3,6-carbazolyl), PNHCZ, obtained from PNTPMCZ, forms iodine complexes with conductivities of 10−1 ohm−1 cm−1 at room temperature. The visible-near-i.r. spectra suggest that the same radical cations responsible for conductivity in poly-N-methyl-(3,6-carbazolyl) are present. Direct comparisons of the structure and physical properties of PTPMCICZ (a predominantly poly-N-hydro-(3,6-carbazolyl) synthesized in liquid iodine) are made.

Synthesis and Characterization of Polyphenothiazene Iodine Complexes

Abstract N-methyl 3,6 dibromophenothiazene has been polymerized by using a nickel complex-assisted Grignard coupling. Vapor phase iodine doping of the organometallic polymerized material led to a conductivity increase of 10−11 ohm−1 cm−1 to 10−5 ohm cm−l at room temperature. The complex thus formed exhibited a semiconductor behavior with a thermal activation energy of 0.1 eV and a strong electronic IR absorbance from 4000–400 cm−1. However, the complexed polymer could be dissolved in liquid I2 and cast into films with air stable, room temperature conductivities as high as 1 ohm−l cm−l. The mechanisms that could give rise to these differences in behavior will be discussed.